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Background
Occupational exposure to live meningococci can potentially cause invasive meningococcal disease in laboratory staff. While, until recently, immunization with quadrivalent polysaccharide vaccine represented one cornerstone of protection, data on long-term persistence of antibodies in adults remain scarce.
Methods
We analyzed the relationship of antibody levels and time following quadrivalent polysaccharide vaccination (Mencevax® ACWY, GlaxoSmithKline) in a cross-sectional sample of 20 laboratory workers vaccinated at ages between 16.4 to 40.7 years from Germany. Sera were obtained 0.4 to 158.5 (median 35.3) months after vaccination. At the time of sampling, laboratory workers had been regularly exposed to meningococci for periods between 3.2 to 163.8 (median 41.2) months. Serum bactericidal assay (SBA) with rabbit complement and a microsphere-based flow analysis method were used to determine bactericidal titers and concentrations of IgG, respectively, against serogroups A, C, W135, and Y. Decay of antibodies was modeled using linear regression. Protective levels were defined as SBA titers ≥ 8.
Results
Half-lives of SBA titers against serogroups A, C, W135, and Y were estimated at 27.4, 21.9, 18.8, and 28.0 months, respectively. Average durations of protection were estimated at 183.9, 182.0, 114.6, and 216.4 months, respectively. Inter-individual variation was high; using lower margins of 95% prediction intervals, minimal durations of protection against serogroups A, C, W135 and Y were estimated at 33.5, 24.6, 0.0, and 55.1 months, respectively. The proportion of staff with protective SBA titers against W135 (65.0%) was significantly lower than proportions protected against A (95.0%), C (94.7%), and Y (95.0%). Consistently, geometric mean titer (97.0) and geometric mean concentration of IgG (2.1 μg/ml) was lowest against serogroup W135. SBA titers in a subset of individuals with incomplete protection rose to ≥ 128 (≥ 8 fold) after reimmunization with a quadrivalent glycoconjugate vaccine.
Conclusions
The average duration of protection following immunization with a quadrivalent polysaccharide vaccine in adults was ≥ 115 months regardless of serogroup. A substantial proportion (approximately 23% according to our decay model) of adult vaccinees may not retain protection against serogroup W135 for five years, the time suggested for reimmunization.
Neisseria meningitidis is a facultative human pathogen that occasionally shows strong resistance against serum complement exposure. Previously described factors that mediate meningococcal serum resistance are for example the capsule, LPS sialylation, and expression of the factor H binding protein. I aimed for identification of novel serum resistance factors, thereby following two approaches, i) the analysis of the impact of global regulators of gene expression on serum resistance; and ii) a comparative analysis of closely related strains differing in serum resistance. (i) Of six meningococcal global regulators of gene expression studied, only mutation of the zinc uptake regulator Zur reduced complement deposition on meningococci. Little was known about meningococcal Zur and regulatory processes in response to zinc. I therefore elucidated the yet unidentified meningococcal Zur regulon comparing the transcriptional response of the N. meningitidis strain MC58 under zinc-rich and zinc-deficient conditions using a common reference design of microarray analysis. The meningococcal Zur regulon comprises 17 genes, of which 15 genes were repressed and two genes were activated at high zinc condition. Amongst the Zur-repressed genes were genes involved in zinc uptake, tRNA modification, and ribosomal assembly. A 23 bp meningococcal consensus Zur binding motif (Zur box) with a conserved central palindrome was established (TGTTATDNHATAACA) and detected in the promoter region of all regulated transcriptional units (genes/operons). In vitro binding of meningococcal Zur to the Zur box of three selected genes was shown for the first time using EMSAs. Binding of meningococcal Zur to DNA depended specifically on zinc, and mutations in the palindromic sequence constrained Zur binding to the DNA motif. ii) Three closely related strains of ST-41/44 cc from invasive disease and carriage which differed in their resistance to serum complement exposure were analysed to identify novel mediators of serum resistance. I compared the strains’ gene content by microarray analysis which revealed six genes being present in both carrier isolates, but absent in the invasive isolate. Four of them are part of two Islands of horizontally transferred DNA, i.e. IHT-B and –C. The working group furthermore applied a comprehensive screening assay, a transcriptome and a proteome analysis leading to identification of three target proteins. I contributed to establish the role of these three proteins in serum resistance: The adhesin Opc mediates serum resistance by binding of vitronectin, a negative regulator of the complement system; the hypothetical protein NMB0865 slightly contributes to serum resistance by a yet unknown mechanism; and NspA, recently identified to bind the negative complement regulator factor H, led to considerable reduced complement-mediated killing.
Entry of Neisseria meningitidis (the meningococcus) into human brain microvascular endothelial cells (HBMEC) is mediated by fibronectin or vitronectin bound to the surface protein Opc forming a bridge to the respective integrins. This interaction leads to cytoskeletal rearrangement and uptake of meningococci. In this study, we determined that the focal adhesion kinase (FAK), which directly associates with integrins, is involved in integrin-mediated internalization of N. meningitidis in HBMEC. Inhibition of FAK activity by the specific FAK inhibitor PF 573882 reduced Opc-mediated invasion of HBMEC more than 90%. Moreover, overexpression of FAK mutants that were either impaired in the kinase activity or were not capable of autophosphorylation or overexpression of the dominant-negative version of FAK (FRNK) blocked integrin-mediated internalization of N. meningitidis. Importantly, FAK-deficient fibroblasts were significantly less invaded by N. meningitidis. Furthermore, N. meningitidis induced tyrosine phosphorylation of several host proteins including the FAK/Src complex substrate cortactin. Inhibition of cortactin expression by siRNA silencing and mutation of critical amino acid residues within cortactin, that encompass Arp2/3 association and dynamin binding, significantly reduced meningococcal invasion into eukaryotic cells suggesting that both domains are critical for efficient uptake of N. meningitidis into eukaryotic cells. Together, these results indicate that N. meningitidis exploits the integrin signal pathway for its entry and that FAK mediates the transfer of signals from activated integrins to the cytoskeleton. A cooperative interplay between FAK, Src and cortactin then enables endocytosis of N. meningitidis into host cells.
Alveolar echinococcosis (AE), a severe and life-threatening disease is caused by the small fox tapeworm Echinococcus multilocularis. Currently, the options of chemotherapeutic treatment are very limited and are based on benzimidazole compounds, which act merely parasitostatic in vivo and often display strong side effects. Therefore, new therapeutic drugs and targets are urgently needed. In the present work the role of two evolutionarily conserved signalling pathways in E. multilocularis, namely the insulin signalling cascade and Abl kinases, has been studied in regard to host-parasite interaction and the possible use in anti-AE chemotherapy.
Introduction: Chronic nonbacterial osteomyelitis (CNO) is an inflammatory disorder of unknown etiology. In children and adolescents CNO predominantly affects the metaphyses of the long bones, but lesions can occur at any site of the skeleton. Prospectively followed cohorts using a standardized protocol in diagnosis and treatment have rarely been reported. Methods: Thirty-seven children diagnosed with CNO were treated with naproxen continuously for the first 6 months. If assessment at that time revealed progressive disease or no further improvement, sulfasalazine and short-term corticosteroids were added. The aims of our short-term follow-up study were to describe treatment response in detail and to identify potential risk factors for an unfavorable outcome. Results: Naproxen treatment was highly effective in general, inducing a symptom-free status in 43% of our patients after 6 months. However, four nonsteroidal anti-inflammatory drug (NSAID) partial-responders were additionally treated with sulfasalazine and short-term corticosteroids. The total number of clinical detectable lesions was significantly reduced. Mean disease activity estimated by the patient/physician and the physical aspect of health-related quality of life including functional ability (global assessment/childhood health assessment questionnaire and childhood health assessment questionnaire) and pain improved significantly. Forty-one percent of our patients showed radiological relapses, but 67% of them were clinically silent. Conclusions: Most children show a favorable clinical course in the first year of anti-inflammatory treatment with NSAIDs. Relapses and new radiological lesions can occur at any time and at any site in the skeleton but may not be clinically symptomatic. Whole-body magnetic resonance imaging proved to be very sensitive for initial and follow-up diagnostics.
Background: Specific cell targeting is an important, yet unsolved problem in bacteria-based therapeutic applications, like tumor or gene therapy. Here, we describe the construction of a novel, internalin A and B (InlAB)-deficient Listeria monocytogenes strain (Lm-spa+), which expresses protein A of Staphylococcus aureus (SPA) and anchors SPA in the correct orientation on the bacterial cell surface. Results: This listerial strain efficiently binds antibodies allowing specific interaction of the bacterium with the target recognized by the antibody. Binding of Trastuzumab (Herceptin®) or Cetuximab (Erbitux®) to Lm-spa+, two clinically approved monoclonal antibodies directed against HER2/neu and EGFR/HER1, respectively, triggers InlABindependent internalization into non-phagocytic cancer cell lines overexpressing the respective receptors. Internalization, subsequent escape into the host cell cytosol and intracellular replication of these bacteria are as efficient as of the corresponding InlAB-positive, SPA-negative parental strain. This specific antibody/receptormediated internalization of Lm-spa+ is shown in the murine 4T1 tumor cell line, the isogenic 4T1-HER2 cell line as well as the human cancer cell lines SK-BR-3 and SK-OV-3. Importantly, this targeting approach is applicable in a xenograft mouse tumor model after crosslinking the antibody to SPA on the listerial cell surface. Conclusions: Binding of receptor-specific antibodies to SPA-expressing L. monocytogenes may represent a promising approach to target L. monocytogenes to host cells expressing specific receptors triggering internalization.
Disruption of the blood-brain barrier (BBB) is a hallmark event in the pathophysiology of bacterial meningitis. Several inflammatory mediators, such as tumor necrosis factor alpha (TNF-a), nitric oxide and matrix metalloproteinases (MMPs), contribute to this disruption. Here we show that infection of human brain microvascular endothelial cells (HBMEC) with Neisseria meningitidis induced an increase of permeability at prolonged time of infection. This was paralleled by an increase in MMP-8 activity in supernatants collected from infected cells. A detailed analysis revealed that MMP-8 was involved in the proteolytic cleavage of the tight junction protein occludin, resulting in its disappearance from the cell periphery and cleavage to a lower-sized 50-kDa protein in infected HBMEC. Abrogation of MMP-8 activity by specific inhibitors as well as transfection with MMP-8 siRNA abolished production of the cleavage fragment and occludin remained attached to the cell periphery. In addition, MMP-8 affected cell adherence to the underlying matrix. A similar temporal relationship was observed for MMP activity and cell detachment. Injury of the HBMEC monolayer suggested the requirement of direct cell contact because no detachment was observed when bacteria were placed above a transwell membrane or when bacterial supernatant was directly added to cells. Inhibition of MMP-8 partially prevented detachment of infected HBMEC and restored BBB permeability. Together, we established that MMP-8 activity plays a crucial role in disassembly of cell junction components and cell adhesion during meningococcal infection.
Neisseria meningitidis is a facultatively pathogenic human commensal and strictly adapted to its niche within the human host, the nasopharynx. Not much is known about the regulatory processes required for adaptation to this environment. Therefore the role of the transcriptional regulator NMB1843, one of the two predicted regulators of the MarR family in the meningococcal genome, was investigated. As this gene displayed a high sequence homology to FarR, the Fatty acid resistance Regulator in N. gonorrhoeae, we designated the meningococcal protein FarR (NmFarR). Homology modeling of this protein revealed a dimeric structure with the characteristic winged helix-turn-helix DNA binding motif of the MarR family. NmFarR is highly conserved among meningococcal strains and expression of farR during exponential growth is controlled post-transcriptionally, being highest in the late exponential phase. By means of electrophoretic mobility shift assays (EMSAs) the direct and specific binding of FarR to the farAB promoter region was shown, comparable to its homologue in gonococci. As FarR is involved in fatty acid resistance in N. gonorrhoeae, susceptibility assays with the medium chain lauric acid (C12:0), the long chain saturated palmitic acid (C16:0) and the long chain unsaturated linoleic acid (C18:2) were performed, testing a wide variety of strains of both species. In contrast to the unusually susceptible gonococci, a high intrinsic fatty acid resistance was detected in almost all meningococcal isolates. The molecular basis for this intrinsic resistance in N. meningitidis was elucidated, showing that both a functional FarAB efflux pump system as well as an intact lipopolysaccharide (LPS) are responsible for palmitic acid resistance. However, even despite circumvention of the intrinsic resistance, FarR could not be connected with fatty acid resistance in meningococci. Instead, FarR was shown to directly and specifically repress expression of the Neisseria adhesin A (nadA), a promising vaccine candidate absent in N. gonorrhoeae. Microarray analyses verified these results and disclosed no further similarly regulated genes, rendering the FarR regulon the smallest regulon in meningococci reported until now. The exact FarR binding site within the nadA promoter region was identified as a 16 bp palindromic repeat and its influence on nadA transcription was proved by reporter gene fusion assays. This repression was also shown to be relevant for infection as farR deficient mutant strains displayed an increased attachment to epithelial cells. Furthermore, farR transcription was attested to be repressed upon contact with active complement components within human serum. Concluding, it is shown that FarR adopted a role in meningococcal host niche adaptation, holding the balance between immune evasion by repressing the highly antigenic nadA and host cell attachment via this same adhesin.
Echinococcus multilocularis is the causative agent of alveolar echinococcosis (AE), a life-threatening disease with limited options of chemotherapeutic treatment. Anti-AE chemotherapy is currently based on a single class of drugs, the benzimidazoles. Although acting parasitocidic in vitro, benzimidazoles are merely parasitostatic during in vivo treatment of AE and cause severe site effects. In the case of operable lesions, the resection of parasite tissue needs to be supported by a prolonged chemotherapy. Thus, the current treatment options for AE are inadequate and require alternatives. In the present work, the flatworm signaling pathways were analyzed to establish potential targets for novel therapeutic approaches. I focused on factors that are involved in development and proliferation of E. multilocularis using molecular, biochemical and cell biological methods. Among the analysed factors were three MAP kinases of the parasite, EmMPK1, an Erk-1/2 orthologue, EmMPK2, a p38 orthologue and EmMPK3, an Erk7/8 orthologue. Further, I identified and characterized EmMKK2, a MEK1/2 orthologue of the parasite, which, together with the known kinases EmRaf and EmMPK1, forms an Erk1/2-like MAPK module. Moreover, I was able to demonstrate several influences of host growth factors such as EGF (epidermal growth factor) and insulin on worm signaling mechanisms and larval growth, including the phosphorylation of Elp, an ezrin-radixin-moesin like protein, EmMPK1, EmMPK3 and increased mitotic activity of Echinococcus cells. In addition, several substances were examined for their efficacy against the parasite including (i) general tyrosine kinase inhibitors (PP2, leflunamide), (ii) compounds designed to inhibit the activity of receptor tyrosine kinases, (iii) anti-neoplastic agents (miltefosine, perifosine), (iv) serine/threonine kinase inhibitors that have been designed to block the Erk1/2 MAPK cascade and (v) inhibitors of p38 MAPKs. In these studies, EmMPK2 proved to be a promising drug target for the following reasons. Amino acid sequence analysis disclosed several differences to human p38 MAPKs, which is likely to be the reason for the observed enhanced basal activity of recombinant EmMPK2 towards myelin basic protein in comparison to human recombinant p38 MAPK-α. In addition, the prominent auto-phosphorylation activity of the recombinant EmMPK2 protein together with the absence of an interaction with the Echinococcus MKKs suggest a different mechanism of regulation compared to the human enzyme. EmMPK2 activity could be effectively inhibited in vitro and in cultivated metacestode vesicles by treatment with SB202190 and ML3403, two ATP-competitive pyridinyl imidazole inhibitors of p38 MAPKs, in a concentration-dependent manner. Moreover, both compounds, in particular ML3403, caused parasite vesicle inactivation at concentrations which did not affect cultured mammalian cells. Likewise, during the cultivation of Echinococcus primary cells, the presence of ML3403 prevented the generation of new vesicles. Targeting members of the EGF signaling pathway, particulary of the Erk1/2-like MAPK cascade, with Raf and MEK inhibitors prevented the phosphorylation of EmMPK1 in metacestodes cultivated in vitro. However, although parasite growth was prevented under these conditions, the structural integrity of the metacestode vesicles maintained during long-term cultivation in the presence of the MAPK cascade inhibitors. Similar results were obtained when studying the effects of other drugs mentioned above. Taken together, several targets could be identified that reacted with high sensitivity to the presence of inhibitory substances, but did not cause the parasite’s death with one exception, the pyridinyl imidazoles. Based on the presented data, I suggest pyridinyl imidazoles as a novel class of anti-Echinococcus drugs and imply EmMPK2 as survival signal mediating factor, the inhibition of which could be used for the treatment of AE.
Introduction: This study investigates the role of Wolbachia bacteria in the pathogenesis of O. volvulus keratitis in a mouse model. Wolbachia bacteria are essential symbionts of most filarial nematodes of importance for mankind. Methods: Using a mouse model for river blindness in which soluble extracts of filarial nematodes are injected in the corneal stroma, changes in stromal thickness and haze of the cornea are observed by in vivo confocal microscopy, followed by immunohistochemical staining for neutrophils and PECAM-1, as well as ELISA of corneal chemokines. Reactions to filarial extracts containing Wolbachia are compared to those without the endosymbiont. Results: The approach of characterizing Wolbachia’s role in river blindness in this study is threefold. Firstly, Wolbachia-depleted extracts from doxycycline treated onchocerciasis patients led to a diminished inflammatory response in corneas of C57BL/6 mice compared to untreated, i.e. Wolbachia containing antigen. The decreased cell recruitment observed with doxycycline treated extracts involved neutrophils, but not eosinophils. This finding demonstrated that the presence of Wolbachia increases neutrophil recruitment. Secondly, extracts from Wolbachia-containing B. malayi revealed markedly more pathology than endosymbiont-free A. viteae antigen. This again pointed at the role of Wolbachia in development of disease. Thirdly, Toll-like Receptor 4 (TLR4) dependence was shown to exist for the inflammatory response to Wolbachia harboring O. volvulus antigen by looking at the corneal pathology in TLR4-mutant C3H/HeJ mice, compared to the wild-type C3H/HeN strain. Investigating further Wolbachia mediated mechanisms of neutrophil recruitment to the cornea, this study also showed that expression of the adhesion molecule PECAM-1 in limbal vessels, as well as upregulation of the CXC chemokines KC and MIP-2 were dependent on the presence of functional TLR4 and Wolbachia respectively. Conclusions: This study indicates that the innate immune system and Wolbachia endobacteria play an important role in the inflammatory response associated with the pathogenesis of onchocerca keratitis, suggesting a complete alteration in our understanding of the immunopathology of filariasis.
Helicobacter pylori (H. pylori) is a gram-negative, microaerophilic, spiral-shaped bacterium. It resides in the gastric mucous layer and epithelial lining of the stomach, often clustering at the junction of epithelial cells. H. pylori colonization usually occurs during childhood, and, when left untreated, generally persists for the host’s lifetime. Persistent H. pylori infection can cause chronic superficial gastritis and gastric duodenal ulcers, which is possibly linked to the development of gastric carcinoma and primary gastric lymphoma, especially of the mucosa-associated lymphoid tissue (MALT) type. It was recently defined as a class 1 carcinogen. The gastric inflammatory response to H. pylori infection is characterized by infiltration of the mucosa by neutrophils, T and B cells, plasma cells and macrophages. This reaction is initially induced by H. pylori attachment, followed by cytokine release by gastric epithelial cells. Epidemiological studies revealed that more than 50% of adults are infected with H. pylori all over the world. However, interestingly, only a subset of individuals develops serious H. pylori-related disease, while most infected individuals show no clinical symptoms. Gastric epithelial cells, like intestinal epithelial cells, express a subset of Toll-like receptors (TLRs) and similar pattern recognition receptors, which are important for the activation of the innate immune system. Bacterial components such as lipopeptides, peptidoglycan, LPS, flagellin, and CpG DNA are the ligands of TLRs. Thus, TLRs in gastric epithelial cells might be able to contribute to innate immune responses to H. pylori infection. However, there is scant knowledge about the mechanisms of innate immune response to acute and chronic H. pylori infection. This study is focused on host cell interaction with H. pylori flagellins, which are major components of the flagellar apparatus, and innate immune responses against them. The flagellins, which are essential for bacterial motility, are important for H. pylori to survive in the stomach mucus during the whole infectious cycle. Flagellins are known to act as the main determinant of many mucosal pathogenic bacteria that mediates proinflammatory signaling, including transcriptional factor NF-B activation via TLR5. In the first part of the study, we investigated the effects of H. pylori flagellins on TLR5 expression, NF-B activation and IL-8 production in various human intestinal and gastric epithelial cell lines by using Western blotting, semi-quantitative RT-PCR and ELISA. IL-8 is a potent neutrophil-activating chemokine expressed by gastric epithelial cells. When we stimulated the cells with the native form of or E. coli-expressed recombinant H. pylori flagellins, FlaA and FlaB, IL-8 was not induced in any case, while S. typhimurium flagellin (FliC) induced it significantly. H. pylori was able to modulate TLR5 protein expression and NF-B activation in epithelial cells regardless of the presence of flagellins. Having established the finding that H. pylori flagellins have unusually low immune-stimulatory properties, we further investigated to find out possible reasons why H. pylori flagellins are distinct from other flagellins of pathogenic bacteria in terms of immune-stimulatory activity. From amino acid sequence comparisons, we found that some regions in the terminal D0D1 protein domains of H. pylori flagellins are different from flagellins of other pathogenic bacteria. D0D1 is the domain which is known to interact with TLR5 in Salmonella FliC. To examine whether the differences endow H. pylori flagellins with low immune-stimulatory properties, we created several mutated H. pylori flagellins (FlaA and FlaB) by site-directed mutagenesis that contain one to four epitopes of Salmonella flagellin D0D1 domain amino acid sequences. The mutant flagellins expressed both in H. pylori and E. coli were used to determine their influence on TLR5-signaling mediators and cytokines, such as MAPkinases, (ERK, p38), NF-B, IL-8, and MIP-3. Salmonella FliC expressed in E. coli induced activation of p38, IB and NF-B leading to IL-8 and MIP-3 production in gastric epithelial cells. However, none of the H. pylori flagellin mutants activated MAP kinases or induced those cytokines. In a co-immunoprecipitation assay none of the recombinant wild type or mutated H. pylori flagellins showed any direct physical interaction with TLR5, while Salmonella FliC significantly co-precipitated with TLR5. Interestingly, we found H. pylori flagellins bind to the surface of gastric epithelial cells like FliC, although they do not bind to or stimulate TLR5. Based on the physical interaction of H. pylori flagellins and FliC with human gastric epithelial cells, we further analyzed transcriptional regulation by H. pylori flagellin in these host cells using microarray analysis. The result showed that H. pylori flagellins modulate host cell gene expression, and many of the identified regulation events overlap with the genes regulated by FliC. These findings imply that H. pylori flagellins do play a role in gene regulation of host cells probably through still unknown factors or receptors, although they do not trigger TLR5-related signaling pathways. The results of our study suggest that, in addition to the low immune-stimulatory activity of H. pylori LPS, the evolutionary reduction in stimulating activity of H. pylori flagellins on the local innate immune responses in the stomach in vivo might be a further strategy of this chronic mucosal pathogen to evade and minimize deleterious host responses, thereby promoting life-long persistence in the host, and possibly contributing to cancerogenesis.
The insulin receptor ortholog EmIR of the fox-tapeworm Echinococcus multilocularis displays significant structural homology to the human insulin receptor (HIR) and has been suggested to be involved in insulin sensing mechanisms of the parasite’s metacestode larval stage. In the present work, the effects of host insulin on Echinococcus metacestode vesicles and the proposed interaction between EmIR and mammalian insulin have been studied using biochemical and cell-biological approaches. Human insulin, exogenously added to in vitro cultivated parasite larvae, (i) significantly stimulated parasite survival and growth, (ii) induced DNA de novo synthesis in Echinococcus, (iii) affected overall protein phosphorylation in the parasite, and (iv) specifically induced the phosphorylation of the parasite’s Erk-like MAP kinase orthologue EmMPK1. These results clearly indicated that Echinococcus metacestode vesicles are able to sense exogenous host insulin which induces a mitogenic response. To investigate whether EmIR mediates these effects, anti-EmIR antibodies were produced and utilized in biochemical assays and immunohistochemical analyses. EmIR was shown to be expressed in the germinal layer of the parasite both on the surface of glycogen storing cells and undifferentiated germinal cells. Upon addition of exogenous insulin to metacestode vesicles, the phosphorylation of EmIR was significantly induced, an effect which was suppressed in the presence of specific inhibitors of insulin receptor-like tyrosine kinases. Furthermore, upon expression of EmIR/HIR receptor chimera containing the extracellular ligand binding domain of EmIR in HEK 293 cells, a specific autophosphorylation of the chimera could be induced through the addition of exogenous insulin. These results indicated the capability of EmIR to sense and to transmit host insulin signals to the Echinococcus signaling machinery. The importance of insulin signaling mechanisms for parasite survival and growth were underscored by in vitro cultivation experiments in which the addition of an inhibitor of insulin receptor tyrosine kinases led to vesicle degradation and death. Based on the above outlined molecular data on the interaction between EmIR and mammalian insulin, the parasite’s insulin receptor orthologue most probably mediates the insulin effects on parasite growth and is, therefore, a potential candidate factor for host-parasite communication via evolutionary conserved pathways. In a final set of experiments, signaling mechanisms that act downstream of EmIR have been analyzed. These studies revealed significant differences between insulin signaling in Echinococcus and the related cestode parasite Taenia solium. These differences could be associated with differences in the organo-tropism of both species.
In the present thesis, two projects on the use of microarray technology for molecular epidemiology of Neisseria meningitidis have been followed. The first one evaluated microarrays based on polymorphism-directed oligonucleotide design for typing of N. meningitidis adopting the multilocus sequence typing (MLST) concept. The number of oligonucleotides needed to cover all known polymorphisms was much lower compared to the number needed if a tiling strategy would have been chosen. Initial experiments using oligonucleotides 28-32 nucleotides in length, revealed that the applied hybridisation protocols were highly specific. However, despite of several optimisation steps, the rate of misidentification of oligonucleotides remained >1.8% in consecutive validation experiments using arrays representing the genetic diversity at three MLST loci. This finding led to the assumption that the high density of polymorphic sites and extensive GC-content variations at N. meningitidis MLST loci hindered the successful implementation of MLST microarrays based on polymorphism-directed oligonucleotide design. In the 1980s, the ET-15 clone emerged within the ST-11 complex of N. meningitidis. This new clone was associated with severe meningococcal disease and outbreaks world-wide. Therefore, the goal of the second project was to identify genetic differences between ET-15 strains and other ST-11 strains using whole genome microarray technology. Three genes encoding hypothetical proteins were identified to be present in all ET-15 strains but absent in other ST-11 strains. This finding together with unpublished observation from our group suggested that several genome alterations occurred before the clonal expansion of the ET-15 clone started. The role that these three genes play in the pathogenicity of the ET-15 clone is unclear. The genome comparisons revealed furthermore that studies of the ET-15 clone displayed approximately two-fold less gene content variation than ST-11 strains not belonging to the ET-15 clone. This finding is in accordance with the recent emergence and clonal expansion of the ET-15 variant.
The role of DNA supercoiling in the coordinated regulation of gene expression in Helicobacter pylori
(2004)
Summary Mechanisms of global gene regulation in bacteria are not well characterized yet. Changes in global or local supercoiling of chromosomal DNA are thought to play a role in global gene silencing and gene activation. In Helicobacter pylori, a bacterium with few dedicated transcriptional regulators, the structure of some promoters indicates a dependency on DNA topology. For example, the promoter of the major flagellar subunit gene flaA (ó28-dependent) has a shorter spacing of 13 nucleotides (nt) in comparison to the consensus promoter (15 nt). Supercoiling changes might be a mechanism of gene-specific and global transcriptional regulation in this bacterium. The aim of this study was to elucidate, if changes in global supercoiling have an influence on global gene regulation in H. pylori, and on the temporal regulation of the flagellar biosynthesis pathway in this organism. In the present work, global DNA supercoiling in H. pylori was visualized for the first time, by determining the supercoiling state of plasmids under different growth conditions. Using this method, we showed that cellular supercoiling was clearly growth phase-dependent in H. pylori. Coinciding with increased supercoiling during the growth phases, transcription of the flaA gene was increased, while the transcription of a second ó28-dependent gene with regular promoter spacing (HP0472) was reduced, supporting the hypothesis that growth phase-dependency of promoters might be mediated by changes of DNA topology. Supercoiling in H. pylori could be influenced in a reproducible fashion by inhibition of gyrase using novobiocin, which led to DNA relaxation and to a concomitant decrease of flaA transcript levels. Promoter spacer mutagenesis of the flaA promoter was performed. With flaA promoters of increased or reduced length, transcription of flaA was reduced, less susceptible to supercoiling changes, and, under specific conditions, inverted as compared to the wild type promoter. Transcriptional interdependence between the coupled topA-flaB genes and flaA was found by analysis of the flaA promoter mutants. Chromosomally linked gyrA-flgR, and topA-flaB genes were all dependent on supercoiling and coregulated with each other. Comprehensive transcript profiling (DNA microarrays) of wildtype H. pylori with and without novobiocin treatment identified a number of genes (10% of total genes), including flagellin, virulence and housekeeping genes, which were strongly dependent on and appeared to be synchronized by supercoiling changes (transcriptional up- or downregulation). These findings indicate a tightly coupled temporal regulation of flagellar biogenesis and metabolism in H. pylori, dependent on global supercoiling. A specific group of genes was also regulated in H. pylori by overexpression of Topoisomerase I, as detected by genome-wide analysis (DNA microarray). The DNA-bending protein HU is thought to be responsible for influencing the negative supercoiling of DNA, through its ability to wrap DNA. HU is encoded by the hup single gene in H. pylori, and constitutively expressed during the whole growth curve. An H. pylori hup mutant was constructed. H. pylori cells lacking HU protein were viable, but exhibited a severe growth defect. Our data indicate that the lack of HU dramatically changes global DNA supercoiling, indicating an important function of HU in chromosome structuring in H. pylori. Transcriptome analyses were performed and demonstrated that a total of 66 genes were differentially transcribed upon hup deletion, which include virulence genes and many other cell functions. The data indicate that HU might act as further important global regulator in H. pylori. Increased gene expression of heat shock proteins and a decreased transcription of the urease gene cluster may indicate a co-ordinated response of H. pylori to changes of environmental conditions in its specific ecological niche, mediated by HU. After the whole genomic sequences of H. pylori strains 26695 and J99 were published, two ORFs (HP0116 and HP0440) were presumptively annotated as topoisomerase I orthologs. HP0116 is the functional H. pylori topoisomerase I (TopA). HP0440 (topA2) was found in only few (5 of 43) strains. Western blot analysis indicated that TopA2 is antigenically different from TopA. TopA2 is transcribed in H. pylori, but the protein must be functionally different from TopA, since it is lacking one functionally essential zinc finger motif, and was not able to functionally complement a TopA-deficient E. coli. Like topA, topA2 was also transcribed in a growth phase-dependent manner. We did not find a function of TopA2 in DNA structuring or topology, but, in the present study, we were able for the first time to establish a unique function for TopA2 in global gene regulation, by comprehensive transcriptome analysis (DNA microarray). Transcriptome analysis showed that a total of 46 genes were differentially regulated upon topA2 deletion, which included flagellar genes and urease genes. These results suggest that TopA2 might act as a novel important regulator of both flagellar biosynthesis and urease in H. pylori.